The cost of the SIM is usually around US$20 plus any minutes you put on it. It's been 3 years since I purchased mine so I can;t say for sure.
The phone must accept a SIM (be a GSM phone) and operate on the Bands available in Jamaica (if it works in the US\Canada it will likely work in Ja).
This what typical SIM looks like in case you don't know what a SIM is:
Attachment 41009
When you buy a phone from your cell phone provider they "lock" the phone so only their SIM cards will work. In most cases once you have fulfilled the contract they will provide the unlock code and instructions. Phones can also be unlocked using nefarious means fairly easily. This could void any warranties and violate agreements you made with your carrier but is fairly common practice. The easiest way to tell if you phone is unlocked is to find someone who has a different cell phone provider then who you purchased the phone from and see if it works in that phone. If you can make\receive calls then the phone is unlocked. If it doesn't then its likely not unlocked.
Some older phones are not GSM and do not accept a SIM card. These types of phones are obsolete.
